Voltage level shifting is sometimes used in electrical systems that include circuits that utilize different voltage levels. For example, in an electrical system that is controlled by a processor (such as a microcontroller), the processor may generate signals having voltage levels that vary between 0 volts and 3.3 volts, whereas circuitry external to the processor may have voltage levels that vary from 0-12 volts.
FIG. 1 is an example of a conventional technique used to shift the voltage level of a signal. Referring to FIG. 1, an input signal can be applied at Vin to a voltage controlled current source (VCCS) which controls the flow of current Iitm through a resistor R. The current Iitm through the resistor R develops an output voltage Vout that is shifted relative to the input signal Vin. Accordingly, the arrangement shown in FIG. 1 employs an input voltage that generates an intermediate current signal (Iitm) which in turn develops an output voltage across the resistor R.
FIG. 2 is a circuit diagram that illustrates a particular level shifting circuit of the type illustrated in FIG. 1. According to FIG. 2, the input signal is provided at Vin at the base of a transistor Q (or gate of a MOSFET Q). The operation of the transistor Q can generate a current through the resistor R to provide a voltage Vitm to the base of each of the transistors Qn and Qp to provide a shifted voltage output Vgd. In operation, when the transistor Q is toggled on/off by the switching of Vin, the intermediate voltage Vitm toggles between a power supply voltage Vcc and a reference voltage Vref (which can be, for example, ground).